Static library builds with VC14 are OK, but shared library builds fail with:

M:\data\boost\boost\boost/fiber/context.hpp(153): error C2492: 'boost::fibers::context::active_': data with thread storage duration may not have dll interface
M:\data\boost\boost\boost/fiber/context.hpp(153): error C2492: 'private: static boost::fibers::context * boost::fibers::context::active_': data with thread storage duration may not have dll interface

I guess since the std says nothing about shared libraries, you're into implementation defined behaviour here?  Do these variables need to be exported from the dll as part of the interface or are they implementation details?